linux-kernel - RE: [PATCH 5/7] I/OAT: Add support for MSI and MSI-X

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Message-ID: <BAE9DCEF64577A439B3A37F36F9B691C02B81B3A@orsmsx418.amr.corp.intel.com>
Date:	Fri, 20 Jul 2007 14:54:29 -0700
From:	"Nelson, Shannon" <shannon.nelson@...el.com>
To:	"Manu Abraham" <abraham.manu@...il.com>,
	"Roland Dreier" <rdreier@...co.com>
Cc:	"Leech, Christopher" <christopher.leech@...el.com>,
	"Waskiewicz Jr, Peter P" <peter.p.waskiewicz.jr@...el.com>,
	<akpm@...ux-foundation.org>, <linux-kernel@...r.kernel.org>,
	<davem@...emloft.net>, <jeff@...zik.org>,
	"Williams, Dan J" <dan.j.williams@...el.com>
Subject: RE: [PATCH 5/7] I/OAT: Add support for MSI and MSI-X

Manu Abraham [mailto:abraham.manu@...il.com] 
>Sorry for being not clear. What i was asking is thus:
>
>A device that has legacy interrupts and MSI-X. I was thinking that if
>MSI-X failed one should fall back to MSI mode (single message), that's
>what i was assuming.
>
>In such a case, i do enable MSI-X mode on the device, when the request
>for 2 ^ n  number of messages (where messages can be a max of 32), If
>the request fails one falls into a single message mode, ie MSI ?
>
>
>> What device do you have in mind?
>
>
>The device that i have in mind is a SAA7160.

Notice our code looks at the return from pci_enable_msix() - it will
give you a hint whether MSI-X is not supported (returns < 0) or you
simply asked for too many (returns > 0).  If the former, then fallback
to legacy; if the latter, try MSI-X with only one interrupt, which
essentially emulates MSI mode.

sln
--
======================================================================
Mr. Shannon Nelson                 LAN Access Division, Intel Corp.
Shannon.Nelson@...el.com                I don't speak for Intel
(503) 712-7659                    Parents can't afford to be squeamish.
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